1. Field of the Invention
This invention relates to clump-removal devices for separating clumps from an air stream which also includes substantially individualized fibers therein. More specifically, this invention relates to clump-removal devices which create a unique interaction of aerodynamic and mechanical forces upon a fiber/clump mix for aiding in separating fibers therefrom.
The term "clump", or "clumps", as used throughout this application, refers to both groups of intertangled fibers and other particulate matter which are undesirably large for inclusion in a fibrous web or batt.
2. Description of the Prior Art
Dry-formed fibrous webs or batts including a large percentage by weight of wood pulp fibers therein are well known in the prior art. These webs are formed by conveying the fibers in an air stream and depositing them in a randomly arranged and intermingled fashion on a foraminous forming surface in the form of a fibrous web or batt. For some uses, such as wipers and cover sheets for sanitary products, the strength and integrity of the web has been enhanced by including a minor proportion, i.e., up to about 25% by weight, of longer, staple-length fibers therein, and by adhesively bonding the fibers together. For other uses, such as internal absorbent components of sanitary products, unbonded fibrous batts including 100% wood pulp fibers have been satisfactorily employed.
As part of the web or batt formation process a densified pulp lap, generally in sheet form, is fed into a fiberizing device in which individual fibers are separated from the lap and directed into an air stream for deposition on a foraminous wire. One fiberizing device which is commonly employed for this purpose is the Joa Fiberizer, manufactured by Joa, Inc. of North Wales, Fl. Regardless of the fiberizing device which is employed, 100% individualization of wood pulp fibers from the lap is not achieved. Specifically, clumps of fibers may be separated from the lap as a unit, and these clumps, along with substantially individualized fibers, are directed through downstream processing equipment and are included in the completed fibrous web or batt. Moreover, other excessively large foreign particles may be included in the lap, and these particles will also be included in the completed web or batt. All of these clumps adversely affect the aesthetic properties of the web or batt, and also provide uncontrolled basis weight and physical property variations.
It is known in the prior art to employ clump-removal devices to remove clumps from an air stream containing a fiber/clump mix, and to direct substantially individualized fibers onto a foraminous forming surface to form a web or batt, as evidenced by the disclosures in U.S. Pat. Nos. 2,720,005, issued to Clark et al.; 3,575,749, issued to Kroyer; 3,581,706, issued to Rasmussen and 3,644,078, issued to Tachibana et al.
The devices disclosed in the Kroyer patent ('749) and the Rasmussen patent ('706) employ rotating impellers closely adjacent the surface of a separating screen member to agitate a fiber/clump mix thereon for the purpose of separating fibers from the clumps to permit their passage through the separating member. The Tachibana et al. patent ('078) discloses several devices which employ rotating brushes closely adjacent the surface of a separating member to agitate a fiber/clump mix for the purpose of separating substantially individualized fibers from the clumps to permit their passage through the separating member. In all of these devices a foraminous forming member is positioned in overlying relationship with the separating member, and a partial vacuum is established through the forming member to aid in directing fibers through the separating member and onto said forming member in the form of a fibrous web or batt.
The movement of a mechanical mixing device, such as an impeller or brush, in close association with a foraminous separating member can cause excessive wear of both the mechanical mixing device and the separating member. This mechanical wear can cause undesirable machine downtime for repair and/or replacement of parts. Moreover, the use of mechanical mixing devices has not been entirely satisfactory in effecting the desired vigorous agitation of a fiber/clump mix to permit efficient separation of individual fibers from the mix for passage through the separating member. In fact, the use of rotating impellers can actually cause fibers to ball up into clumps that will not pass through the separating member.
U.S. Pat. No. 2,720,005, issued to Clark et al., discloses an air scrabbler system in which jets of air are directed against the interior surface of a foraminous, stationary housing to agitate, or sift, substantially individualized fibers within the housing to permit them to pass through the housing wall and onto a foraminous forming member. This device is not intended for use in handling a fiber/clump mix. Specifically, if clumps are directed into the housing and are not broken up they will not pass through the housing wall, and eventually will block the openings in the wall to impair the operation of the device. Stating this another way, the Clark et al. device is not at all concerned with removing clumps from an air stream containing a fiber/clump mix, and in fact, the Clark et al. device will have to be stopped periodically so that clumps which remain in the inside of the housing can be manually removed. The only function that the Clark et al. device is intended to perform is to sift fibers which are already individualized so that they will pass through the stationary housing onto a forming surface.